1. Field of the Invention
The present invention relates to a device for forming and sealing the openings in a web used for packaging containers for liquid food such as milk, etc.
2. Prior Art
Paper containers commonly called "packaging" containers as shown in FIG. 12 and 16 are used for vending juice, milk, etc. As shown in FIG. 15, a packaging web 1 for such a container is usually made up of support paper 1.sub.1 with a metal foil layer 1.sub.2 such as aluminum foil on one side; the surface of the metal foil layer 1.sub.2 and the other surface of the paper 1.sub.1 being laminated with a thin polyethylene layer 1.sub.3.
At least three types of packaging containers are known to meet the demands of the market:
The first type (see FIG. 16) is a container with a straw hole 6 provided on the top surface, in which the straw hole 6 as seen in FIG. 16, is closed beforehand by laminating it with a polyethylene layer 1.sub.3 and a metal layer 1.sub.2 so that the liquid food-stuff inside may easily consumed using a straw by piercing the closed straw hole with a straw;
The second type of container is one in which a triangle flap on the upper corner of the container is raised and cut with scissors to form a liquid-outlet hole; and
The third type is a container with a liquid-outlet hole covered with a pull-tab 7a as shown in FIG. 12. In this type of container, the hole 5 is punched out and the inner portion of the liquid-outlet hole 5 is sealed with a strip tape 2 to make the container liquid-tight. The pull-tab 7a is heat-sealed on the outside of the container so that the liquid-outlet hole 5 is opened when the pull-tab 7a is peeled off of the container along with the strip tape 2 which the punch hole from inside of the container.
In order to form the straw hole 6 on the container, conventional devices use the following method: Folding lines are first provided on a long, rolled paper of a prescribed width, and after forming an opening (small diameter punch hole 6) to be used as a straw hole at regular intervals 1, the polyethylene layer 1.sub.3 is laminated on one side of the base paper 1.sub.1 and the aluminum layer 1.sub.2, and a polyethylene layer 1.sub.3 on top of it are laminated on the other side of the base paper 1.sub.1 by a laminating machine so that the punch hole 6 is closed (see FIG. 13 and FIG. 15). Thus, a web 1 is formed, and this web is supplied to the packing machine. One side edge of the web 1 continuously carried to the filling section is heated, and then a strip tape 3, that covers the edge of the web 1 when forming the web 1 into a cylindrical shape by connecting the two edges in the longitudinal direction of the web, (see FIG. 14) and thus forming the web into a cylinder while continuously running. After the containers are filled, the web 1 is cut to form individual packaging containers with straw hole openings. The above mentioned process also applies to the type of container which has a liquid-outlet opening which is opened by cutting with scissors, except that this type of container does not have a straw hole.
For a container having a pull-tab, folding lines are formed on a long rolled paper without opening the liquid-outlet, and the paper is formed into a packaging web 1 by laminating it as described above (see FIG. 8 wherein the folding lines of the web 1 are omitted). The pull-tab opening device is formed at a prescribed position on the packaging web 1 that is being intermittently conveyed. The web 1 having with the opening device is folded while the web 1 is continuously conveyed, and both edges of the web 1 in the longitudinal direction are pasted, after which it is filled with a liquid food-stuff, cut and formed to make a container.
In this case, the opening device is formed on the web 1 so that the intermittently conveyed web 1 provided with punch holes 5 which make up the liquid-outlet with constant intervals of 1 (see FIG. 9). After a wide strip tape 2 that covers the punch hole 5 is overlapped and heated and deposited at a prescribed position on one edge of the pierced web (see FIG. 10), and a pull-tab 7a of a prescribed length is joined by heat to the back of the web to close the punch hole 5 (see FIG. 11).
For heating and depositing the strip tape 2 on the web 1, a high-frequency induction heat coil is currently used. For connecting the pull-tab 7a to the web 1, a pull-tab 7a is cut out from the pull-tab tape and joined by heat on the bottom surface of the web 1. This is accomplished between a heating body equipped with a cutting means which moves up and down synchronously with an intermittently moving web 1 and a receptacle positioned above the path of the web 1.
When manufacturing containers having straw holes and containers having the liquid-outlet opening which is cut to open, at the time when the strip tape 3 is pasted, the packaging web 1 is continuously conveyed with the folding lines of the web adjusted with the web conveyance timing. When pull-tab containers are manufactured, on the other hand, since a pull-tab is provided on a web while the web is continuously conveyed (though in the filling section the folding lines of the web is adjusted with the web conveyance timing), the web is conveyed intermittently in the pull-tab mounting section. Accordingly, it is difficult for one machine to manufacture containers with different types of openings, that is, pull-tab openings and non-pull-tab openings.
For non-pull-tab opening containers such as those having a straw hole opening, there is no need to form a hole for the pull-tab opening device or to cover such opening; therefore, a narrow strip tape is used. For pull-tab opening containers, however, in addition to the original purpose of pasting both edges of the web, a strip tape is used to seal the liquid-outlet hole. Thus, a wide strip tape is used. Moreover, the pull-tab must be pasted from a direction opposite to the side where the strip tape is pasted, and for this purpose, additional devices are required in the web conveyance path which leads to the filling section of the packing machine.
In other words, a packing machine with an opening formation device to form a pull-tab opening device and a machine with a simple strip tape pasting device are both required.
It is possible to modify a machine having a simple strip tape pasting device into a machine having a pull-tab opening formation device with optional equipment, but such a modification is not easily done.